Catechol functional groups are of broad interest to the polymer community due to their unique physical and chemical bonding behavior, having the potential to serve as adhesive or toughening moieties in various soft material systems. Catechols have been introduced into macromolecules in various strategies. See for example, Farure et al., Progess in Polymer Science, 38(1):236-270 (2012). A common approach is to couple the amino acid L-3,4-dihydroxyphenylalanine (DOPA) to polymers via carboxylic acid or amine-containing sidechains. See Holten-Andersen, et al. PNAS, 108(7):2651-2655 (2011). Alternatively, a number of vinyl-based monomers with protected or unprotected catechol substituents have been polymerized directly under free radical conditions.
However, one major difficulty of polymerizing catechol-functionalized monomers is control over their solubility in water at physiological pH when targeting high fractions of catechol. Homopolymers of some vinyl-based catechol-containing monomers are typically reported to be insoluble in water below a pH of approximately 10. See Guvendiren et al., Biomacromolecules 9(1):122-128 (2008). Solubility is also an issue for post-functionalized polymers, as a large conversion of acid or amine sidechains can lead to chain collapse under aqueous conditions at mild pH. Nevertheless, a number of applications for lightly-to-moderately-functionalized catechol polymers are actively being explored, including the development of PEG-based tissue adhesives for wound sealing during surgical operations. See Bilic et al., American Journal of Obstetrics and Gynecology, 202(1):85.e1-85.e9 (2010).
When oxidized, catechols can couple to themselves, or react with various nucleophiles present in extracellular matrix proteins on the tissue surface. Thus, catechol-functionalized polymers may be used in many diverse applications, including biological and chemical sensing (See Ruan et al., Sensors and Actuators B: Chemical. 2013, 177: 826-832), incorporation into polyelectrolyte multilayers (See Min et al., Chem. Mater. 2011, 23 (24): 5349-5357), as components of antifouling strategies, and as adhesives for marine and biomedical applications (See Lee et al., Annu. Rev. Mater. Res. 2011 41: 99-132). Retaining the ability to process the highly-functionalized polymers under aqueous, physiological conditions will be transformative for many of these application areas. Water-processable, catechol-functionalized polymers in use today typically are synthesized via post-functionalization of a water-soluble polymer. Because the catechol moiety itself is insoluble except under strongly basic conditions (pH>10), this generally leads to an upper limit on the catechol content of these polymers.
Therefore, there is a need for a highly soluble, catechol-rich polymer that can be synthesized without interfering with the catechols' ability to form reversible and irreversible intermolecular bonds.